With his upbringing in Mandal and the proximity to the sea, it is often the coastal landscapes that we associate with Nielsen. With training from Hans Gude and then in the landscape class at the Düsseldorf Academy, Nielsen's motifs are detailed depictions of coastal environments. The motifs are often unpretentious and spontaneous, with a special ability to capture the effect of light on the surface of the sea. The landscapes therefore acquire a freshness and matter-of-factness that we do not necessarily associate with the romanticism of the Düsseldorf school. But it is not only the sea that caught Nielsen's attention; his ability to depict the coastal towns' environment has given his motifs a great cultural-historical value in the depiction of trade, work, and social conditions.